gistfile1.php

via http://wordpress.stackexchange.com/questions/2623/include-custom-taxonomy-term-in-search/5404#5404

function atom_search_where($where){
  global $wpdb;

  if ( is_search() )
    $where .= "OR (t.name LIKE '%".get_search_query() . "%' AND {$wpdb->posts} . post_status = 'publish')";

  return $where;
}

function atom_search_join($join){
  global $wpdb;

  if ( is_search() )
    $join .= "LEFT JOIN {$wpdb->term_relationships} tr ON {$wpdb->posts}.ID = tr.object_id INNER JOIN {$wpdb->term_taxonomy} tt ON tt.term_taxonomy_id=tr.term_taxonomy_id INNER JOIN {$wpdb->terms} t ON t.term_id = tt.term_id";
  return $join;
}

function atom_search_groupby($groupby){
  global $wpdb;

  // we need to group on post ID
  $groupby_id = "{$wpdb->posts} . ID";
  if ( ! is_search() || strpos($groupby, $groupby_id) !== false )
    return $groupby;

  // groupby was empty, use ours
  if ( ! strlen( trim($groupby) ) )
    return $groupby_id;

  // wasn't empty, append ours
  return $groupby . ", " . $groupby_id;
}

add_filter('posts_where', 'atom_search_where');